Odd, glitchy shadows (Blender Internal)
The blocky shadows are either caused by a low resolution shadow buffer or your object doesn't have enough geometry for the shadow to disperse and appear smooth.

Go to the lamp and under Shadow, increase the size value of the lamp. While you are there, try tweaking the other setting as well to get even better results (hover over the tooltips to see what they do). If not, try subdividing the model a bit, notice the shadow the heads casts on the flat chair shape behind is smooth.
Size: 128

Size: 1024